This section provides background information related to the present disclosure which is not necessarily prior art.
A conventional ethylene oligomerization technology is a catalyst technology for producing various α-olefins with Schulze-Flory or Poisson distribution and is also referred to as a full-range catalyst technology in the art. A catalyst technology for more selectively producing 1-butene, 1-hexene, or 1-octene is also referred to as an on-purpose technology. In recent years, a catalyst technology for more selectively producing 1-hexene or 1-octene has been greatly advanced.
The use of 1-butene, 1-hexene, or 1-octene has been greatly expanded to function as a co-monomer in production of linear low-density polyolefin. The use of the other various α-olefins having 10 or more carbon atoms is being expanded to serve as materials of detergent alcohols, lubricants for oil field, or wax, and the amount of the other α-olefins used is being greatly increased. The full-range catalyst technology has a long history, and a representative example thereof is a Ni-based catalyst being used in a SHOP processor developed by Shell. In this regard, EP0,177,999 and U.S. Pat. No. 3,676,523 illustrate a catalyst system from a diphenylphosphino acetic acid ligand and a Ni compound, and U.S. Pat. No. 4,528,416 illustrates a method of oligomerization of the catalyst in a mono-alcohol or diol solvent. Besides, DE1,443,927 and U.S. Pat. No. 3,906,053 illustrate a method of oligomerization of ethylene under a high ethylene pressure using a trialkyl aluminum catalyst. A method of oligomerization of ethylene with a catalyst system including zirconium alkoxide, alcohol, and an aluminum compound in the presence of solvents of toluene, cylcohexane, and normal-octane is illustrated in U.S. Pat. No. 6,930,218. However, the above-described catalysts have relatively low catalytic activity. EP0,444,505 discloses a processor for producing α-olefin using a Ziegler catalyst. The production of α-olefin is carried out efficiently but requires a relatively high ethylene pressure and a high temperature.
In recent years, the on-purpose catalyst technology of selectively trimerizing or tetramerizing ethylene into 1-hexene or 1-octene using various catalyst technologies has been greatly advanced, and most catalysts are based on chromium catalysts. As disclosed in U.S. Pat. Nos. 5,198,563, 5,376,612, and EP0,608,447, a high-activity and high-selectivity ethylene trimerization catalyst system commercialized by Phillips is based on a trivalent chromium compound, a pyrrole compound, and aluminum alkyl. In recent years, it has been disclosed that a chromium-based catalyst containing a chelate ligand including hetero atoms of phosphorous and nitrogen selectively trimerizes or tetramerizes ethylene into 1-hexene or 1-octene (U.S. Pat. No. 7,964,763), and examples of the catalyst include (phenyl)2PN(isopropyl)P(phenyl)2. The above-described prior art technologies are limited to the selective production of mainly 1-hexene or 1-octene α-olefin with a chromium catalyst containing a chelate ligand including hetero atoms and the chelate ligand is limited to a PNP backbone structure such as (R1)(R2)P—N(R5)—P(R3)(R4). Also, a high-selectivity tetramerization catalyst system is disclosed in KR1,074,202 and based on a catalyst system including a chromium compound, a di-phosphine ligand with a —P—C—C—P— backbone structure, and a co-catalyst compound.
As can be seen from the above description, the development of the full-range or on-purpose α-olefin production technology has been based on the advancement of various catalyst technologies, particularly a new ligand structure, and various requirements of α-olefins for development of various applications and uses need an improved catalyst and an improved process for producing ethylene oligomers.